Check If a Word Occurs As a Prefix of Any Word in a Sentence

Given a sentence that consists of some words separated by a single space, and a searchWord.

You have to check if searchWord is a prefix of any word in sentence.

Return the index of the word in sentence where searchWord is a prefix of this word (1-indexed).

If searchWord is a prefix of more than one word, return the index of the first word (minimum index). If there is no such word return -1.

A prefix of a string S is any leading contiguous substring of S.

Example 1:

Input: sentence = "i love eating burger", searchWord = "burg"

Output: 4

Explanation: "burg" is prefix of "burger" which is the 4th word in the sentence.

Example 2:

Input: sentence = "this problem is an easy problem", searchWord = "pro"

Output: 2

Explanation: "pro" is prefix of "problem" which is the 2nd and the 6th word in the sentence, but we return 2 as it's the minimal index.

Example 3:

Input: sentence = "i am tired", searchWord = "you"

Output: -1

Explanation: "you" is not a prefix of any word in the sentence.

Example 4:

Input: sentence = "i use triple pillow", searchWord = "pill"

Output: 4

Example 5:

Input: sentence = "hello from the other side", searchWord = "they"

Output: -1

Constraints:

1 <= sentence.length <= 100

1 <= searchWord.length <= 10

sentence consists of lowercase English letters and spaces.

searchWord consists of lowercase English letters.

Solution:

using System;
using System.Collections.Generic;
using System.Text;

namespace LeetCode.AskGif.Easy.String
{
 public class IsPrefixOfWordSoln
 {
 public int IsPrefixOfWord(string sentence, string searchWord)
 {
 var word = 1;
 bool isBeginingOfWord = true;
 for(int i = 0; i < sentence.Length; i++)
 {
 if (isBeginingOfWord)
 {
 isBeginingOfWord = false;
 if (IsWordAPrefix(sentence, searchWord, i))
 {
 return word;
 }
 word++;
 }
 if(sentence[i] == ' ')
 {
 isBeginingOfWord = true;
 }
 }
 return -1;
 }

 private bool IsWordAPrefix(string sentence, string searchWord, int i)
 {
 for(int j = 0; j < searchWord.Length; j++)
 {
 if(sentence[i+j] != searchWord[j])
 {
 return false;
 }
 }

 return true;
 }
 }
}

Time Complexity: O(n)

Space Complexity: O(1)

Unit Tests:

using LeetCode.AskGif.Easy.String;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
using System.Collections.Generic;
using System.Text;

namespace CodingUnitTest.Easy.String
{
 [TestClass]
 public class IsPrefixOfWordSolnTests
 {
 [TestMethod]
 public void IsPrefixOfWordSoln_First()
 {
 var sentence = "i love eating burger";
 var searchWord = "burg";
 var output = 4;
 var res = new IsPrefixOfWordSoln().IsPrefixOfWord(sentence, searchWord);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void IsPrefixOfWordSoln_Second()
 {
 var sentence = "this problem is an easy problem";
 var searchWord = "pro";
 var output = 2;
 var res = new IsPrefixOfWordSoln().IsPrefixOfWord(sentence, searchWord);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void IsPrefixOfWordSoln_Fourth()
 {
 var sentence = "i use triple pillow";
 var searchWord = "pill";
 var output = 4;
 var res = new IsPrefixOfWordSoln().IsPrefixOfWord(sentence, searchWord);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void IsPrefixOfWordSoln_Third()
 {
 var sentence = "i am tired";
 var searchWord = "you";
 var output = -1;
 var res = new IsPrefixOfWordSoln().IsPrefixOfWord(sentence, searchWord);

 Assert.AreEqual(res, output);
 }

 [TestMethod]
 public void IsPrefixOfWordSoln_Fifth()
 {
 var sentence = "hello from the other side";
 var searchWord = "they";
 var output = -1;
 var res = new IsPrefixOfWordSoln().IsPrefixOfWord(sentence, searchWord);

 Assert.AreEqual(res, output);
 }
 }
}